1. Technical Field
The present invention relates to an electro-optic device, a method for manufacturing the same, and an electronic apparatus, and particularly, it relates to a structure of an electro-optic device suitable as a display device comprising a light reflecting layer.
2. Related Art
A liquid crystal display device, which is an electro-optic device, is widely used as display means provided on various electronic apparatuses. The liquid crystal display device has a basic cell structure in which a liquid crystal is sealed between a pair of substrates. A reflective liquid crystal display device partially using external light as display light is generally known as such a liquid crystal display device and conventionally mainly used for a portable electronic apparatus. In recent years, a transflective liquid crystal display device capable of a transmissive display using a black light in the dark and a reflective display using external light in lit areas has been provided in the market.
In the reflective liquid crystal display device or transflective-liquid crystal display device, a reflecting layer is frequently provided on the back side (opposite to the observation side) of a liquid crystal in the basic cell structure. The reflecting layer generally comprises a metal thin film of aluminum or the like. In the transflective liquid crystal display device, the reflecting layer has an aperture (window) provided for each pixel to transmit light emitted from the backlight through the apertures for transmissive display. In some cases, the reflecting layer is formed as a reflecting electrode having the function of an electrode for applying an electric field to the liquid crystal, or a transparent electrode layer or the like is provided separately from the reflecting layer so that the reflecting layer has only a light reflecting function.
However, a relatively small liquid crystal display device used for a cellular phone or the like has recently been required to display a color image and have higher definition, and thus the reflective or transflective liquid crystal display device has been required to make brighter reflective display. Therefore, as a material for the metal thin film used for forming the reflective layer, a silver alloy having higher reflectance than that of aluminum, such as an APC (Ag—Pd—Cu) alloy or the like, has recently been used. The silver alloy has low electric resistance, and is thus used as a material for electrodes and wirings. However, the APC alloy generally has low water resistance and thus has a problem in which metal is dissolved from a patterned thin film comprising the APC alloy due to ionization by contact with hot water in the manufacturing process, and electromigration or electric corrosion occurs due to an applied voltage.
Also, the silver alloy generally has low adhesion to glass substrates and thus has a difficulty in forming the reflecting layer directly on the substrate. In this way, the use of a single APC alloy causes various problems. Therefore, a method for providing a laminated structure comprising the reflecting layer and an ITO (Indium Tin Oxide) layer provided above or below the reflecting layer has been proposed for preventing these problems.
When only an alignment film is disposed between the silver alloy and the liquid crystal, the above-described conventional liquid crystal display device is known to have a problem in which a polarity deviation occurs due to a difference in material from a counter transparent electrode, and the silver alloy is dissolved in the liquid crystal. Therefore, it is conceivable that a method comprising laminating a thin film of a conductive metal oxide such as ITO or the like on a silver alloy film to provide a laminated structure is used. However, this method has the problem of easily producing a shape abnormality such as a hillock due to the stress applied from an upper layer and a heating process for forming the upper layer. Therefore, when the silver alloy film is used for an electrode and wiring, an electrical short circuit easily occurs due to the shape abnormality, thereby deteriorating electrical reliability and the yield of the manufacturing line.
Particularly, in forming a sectional structure in which a silver alloy film is held between upper and lower ITO films, the thickness of the upper ITO film provided above the silver alloy film must be significantly increased for completely covering the side surface of the step formed by the thickness of the silver alloy film. Therefore, the internal stress of the upper ITO film is increased, and thermal stress of heating also occurs due to a difference between the thermal expansion coefficients of the silver alloy film and the ITO film, thereby causing the problem of further increasing the stress concentration in the silver alloy film. The internal stress and thermal stress are thought to be a main cause of the shape abnormality such as a hillock or the like in the silver alloy film.
The present invention has been provided for solving the above problems, and an object of the present invention is to provide an electro-optic device comprising a reflecting layer composed of silver only or a silver alloy and having a structure capable of decreasing the occurrence of a shape abnormality such as a hillock or the like in the reflecting layer.